Foil bearings are currently used in a limited number of applications involving high-speed rotary machines. The use of relatively intricate processes to form metal foils, undersprings, and other components of the bearings results in high manufacturing cost. The use of thermoplastics rather than metals for construction of foil bearings has been proposed as a means for decreasing that cost.
In conventional electrical machines which employ foil bearings, the bearings are mounted on support members which are positioned outboard of the armature. This results in a relatively long rotor shaft. The first bending critical speed of the rotor shaft (i.e. the rotational speed at which bending of the shaft occurs as a result of resonance) is inversely related to its axial length. Often, the desired operating speed of the machine cannot be achieved without encountering the bending phenomenon, and the machine must be operated at a speed lower than that desired in order to maintain an acceptable critical speed margin.
This invention is directed in part to heretofore unrecognized advantages associated with alternative positioning of foil bearings in electrical machines. Specifically, an object of the invention is to reduce and optimize the axial length of such machines, thus extending their safe operating speeds and providing the further advantages of increased compactness and decreased weight.
Another object of the invention is to provide a novel winding assembly adapted for use in certain embodiments of the invention.
A further object of the invention is to provide a novel stator assembly adapted for use in other embodiments of the invention.